Applied ischemia during 4 weeks of lower limb suspension did not preserve strength but attenuated lateral gastrocnemius atrophy (4.7% vs 10.2% in controls) and abolished CMAP slowing.
Does applied ischemia prevent muscle atrophy and strength loss in adults undergoing prolonged lower limb unweighting?
Applied ischemia during prolonged limb unweighting partially preserves muscle cross-sectional area and prevents slowing of the compound muscle action potential, though it does not preserve strength.
Absolute Event Rate: 4.7% vs 10.2%
Strength loss following disuse may result from alterations in muscle and/or neurological properties. In this paper, we report our findings on human plantar flexor muscle properties following 4 wk of limb suspension (unilateral lower limb suspension), along with the effect of applied ischemia (Isc) on these properties. In the companion paper (Part II), we report our findings on the changes in neurological properties. Measurements of voluntary and evoked forces, the compound muscle fiber action potential (CMAP), and muscle cross-sectional area (CSA) were collected before and after 4 wk of unilateral lower limb suspension in adults (n = 18; 19-28 yr). A subset of subjects (n = 6) received applications of Isc 3 days/wk (3 sets; 5-min duration). In the subjects not receiving Isc, the loss in CSA and strength was as expected ( approximately 9 and 14%). We observed a 30% slowing in the duration of the CMAP, a 10% decrease in evoked doublet force, a 12% increase in the twitch-to-doublet force ratio, and an altered postactivation potentiation response (11% increase in the postactivation potentiation-to-doublet ratio). We also detected a 10% slowing in the ability of the plantar flexor to develop force during the initial phase of an evoked contraction, along with a 6% reduction in in vivo specific doublet force. In the Isc subjects, no preservation was observed in strength or the evoked muscle properties. However, the Isc group did maintain CSA of the lateral gastrocnemius, as the control subjects' lateral gastrocnemius atrophied 10.2%, whereas the subjects receiving Isc atrophied 4.7%. Additionally, Isc abolished the unweighting-induced slowing in the CMAP. These findings suggest that unweighting alters the contractile properties involved in the excitation-contraction coupling processes and that Isc impacts the sarcolemma.
Clark et al. (Fri,) conducted a other in Prolonged unweighting (n=18). Applied ischemia vs. No applied ischemia was evaluated on Lateral gastrocnemius atrophy. Applied ischemia during 4 weeks of lower limb suspension did not preserve strength but attenuated lateral gastrocnemius atrophy (4.7% vs 10.2% in controls) and abolished CMAP slowing.
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